Electronic devices are known to emit radiation in the form of electromagnetic interference. In an office environment in which several electronic devices coexist, radiation emitted from one device is likely to affect the electronic signal of another device. It is therefore necessary to suppress electromagnetic interference (EMI) by preventing radiation of unwanted radio frequency energy. Conductors in cables connecting electronic devices can serve as radiating elements. To prevent this type of radiation, the EMI carried by these conductors may be attenuated by placing ferrite suppressor beads on the cables at the point of egress from a device that is producing EMI.
Ferrite materials have been found to be extremely effective in suppressing EMI. Ferrite suppressors are magnetic ceramic materials characterized by high magnetic permeability and high electrical resistivity. Ferrite beads, which are illustrated in "FAIR-RITE LINEAR FERRITES", 10th Edition September 1986, distributed by Fair-Rite Products Corporation of Wallkill, N.Y., are produced in a variety of configurations including cylindrical beads, toroid beads and multi-hole beads, all of which are particularly suited for shielding conductive wires from EMI. When a suitable ferrite bead is inserted into a circuit containing d.c. and/or useful signals as well as noise or interference, the desired signals will pass through, while undesirable energy is attenuated. This is accomplished through the impedance of the ferrite bead which is frequency sensitive.
Flat cables are generally composed of a plurality of insulated electrical conductors. The number of conductors can vary from 3 to 4 up to 60 or more. Commonly, the distance between the axial centers of adjacent conductors, or the pitch of the cable, is equal to 0.050 inches. Flat cable configurations promote convenient termination at gang plugs and sockets and are extremely useful in devices having moveable parts in which conductors can become entangled. It is often desirable to suppress EMI in flat cables. Ferrite beads for flat cable come in several configurations. One flat cable suppressor is a one-piece member comprising a rectangular box-like bead having a rectangular path extending therethrough. Another configuration of a flat cable EMI suppressor is the split ferrite bead comprising upper and lower generally rectangular members each having a U-shaped channel disposed therein respectively. The rectangular members are assembled so that the U-shaped channels are opposed and aligned to define a pathway for the flat connector cable. The design of the split ferrite bead is particularly suited for simple retrofits to equipment in both the field and in designing stages. In the past, the two halves of the split ferrite bead were held in intimate contact about a flat cable by a pair of U-shaped clamping clips.
Although split ferrite beads are desirable for flat cables comprising twenty or more conductors, angular shifting within the bead of cables comprising only a few conductors does occur. The movement of the flat cable within the split ferrite bead is undesirable since the impedance encountered by the signal in each of the individual conductors of the flat cable will vary along the width of the cable as it passes through the bead.
Accordingly, it is the primary object of the subject invention to provide a dielectric housing or case for a split ferrite bead having means for prohibiting lateral movement and angular shifting of a flat conductor cable extending therethrough.
It is a further object of the subject invention to provide a split ferrite bead case having means to prevent the case from sliding along the length of a flat cable conductor extending therethrough.
It is still a further object of the subject invention to provide a split ferrite bead case having means for promoting quick and easy access to a flat conductor cable extending therethrough.